This invention relates to a fluid velocity measuring device. More particularly, it relates to a fluid velocity measuring device wherein oscillating rotary forces on the device arising from the shedding of vortices created by the passing of a freestream of fluid around the device and translational drag forces on the device are detected by piezoelectric sensor crystals which create electric signals from which fluid velocity components of speed and direction are deduced by an electric circuit. Previously, the measurement of freestream fluid flow velocity was accomplished by the utilization of two separate instruments: one to measure flow speed, e.g. pitot-static tube, venturi tube, bridled pressure plate; and the other to measure flow direction, e.g. directional vane (wind vane, weather vane). The present invention measures freestream flow velocity with a single device.
The utilization of the vortex street phenomenon as an indication of fluid speed is well known in the prior art. When a body is placed in a stream of fluid flow with a Reynolds number between 10.sup.2 and 10.sup.5, vortices are shed alternately from either side of the body at a frequency proportional to the speed of fluid flow.
The prior art, however, limits the application of the vortex street phenomenon to flow inside a conduit with the relationship between vortex creation frequency and fluid speed being dependent upon the conduit diameter. The present invention imposes no such requirement and may be mounted in a freestream of fluid such as the air for measuring wind velocities, or in a wind tunnel for measuring air stream perturbations created by aircraft wings and fuselages, or in the ocean or river for measuring water current velocities. The present invention measures vortex creation frequency at the point of creation whereas prior art devices counted the vortex creation frequency at a remote spot somewhat downstream. Downstream counting may lead to unacceptable accuracy since extraneous currents may induce error. Furthermore, downstream counting is impractical in a freestream since the counter would require repositioning for each change in fluid flow direction. One known device which utilizes temperature sensors to determine vortex creation frequency at the point of creation requires precision aligning and it is impractical for use in a freestream fluid. Some advantages of the present invention are, firstly, the consolidation of the functions of both of these types of instruments into one simple solid state device with no moving parts, and secondly, that both flow speed and flow direction can be measured at the same time at the same place.
An object of the present invention is a fluid velocity measuring device adapted to accurately measure freestream fluid flow speed and direction utilizing translational drag and vortex formation phenomenon.
A further object of this invention is a fluid velocity measuring device which yields the foregoing advantages and which also measures fluid flow speed and direction at the same time and at the same place.
A further object of this invention is a fluid velocity measuring device which yields the foregoing advantages and which is simply constructed and easy to operate.
Other objects and advantages of the present invention will be readily apparent from the following description and drawings which illustrate a preferred embodiment of the present invention.